4.4 Scope Rules

• The scope of a name is the part of the program within which the name can be used
• For an automatic variable declared at the beginning of a function, the scope is the function in which the name is declared. Local variables of the same name in different functions are unrelated
• The scope of an external variable or a function lasts from the point at which it is declared to the end of the file being compiled  
• It is important to distinguish between the declaration of an external variable and its definition
• A declaration announces the properties of an external variable (primarily its type) (ie. extern int a;)
• A definition also cause storage to be set aside (ie. int a;)
• Array size must be specified with the definition, but are optional with an extern declaration
• Initialization of an external variable goes only with the definition
• Example: